22 Tool Fail
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Transcript of 22 Tool Fail
Understanding Tool Failures Tool Analysis
• Working Environment• Areas of Tool Failure• Piston Impact Area• Blank firing • Fatigue • Seizures• Bending• Tool Tip• Brittle• Modifications• Manufacturing Defects• Extending Tool Life
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Working Environment
Mechanical SurfaceDamages
Impact loads (from piston)
Torsion
BendingPressure & Heat
Seizures
External Factors:- Temperature- Corrosion- Mechanical Surface Damage- Wear and Tear- Dirt
Axial Loads(Compression)
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Bushing area - Upper Top of Tool
Retainer pin area
Bushing area - Lower
Working area
Tip of Tool
DeformationChipped Edges
FatigueSeizuresExcessive bushing wear
FatigueSeizuresBlank firingWorn retainer pinsExcessive bushing wear Fatigue
SeizuresBendingExcessive bushing wear
FatigueBendingMechanical damages i.e. deep gouges
Tip breakage MushroomingWrong tool in application
Areas of Tool Failure
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Piston damage • Deformation is caused by:
- Improper impact energy - oil flow and pressure.- High working temperature (e.g. foundries)
• Chipping or corner loading is caused by:- Excessively worn bushings.
• Common failure of pirate tools• Tools with a deformed or chipped top edge will cause piston failure.
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Piston Impact Area
Blank Firing
Blank Firing occurs where tool is not properly preloaded. - Impact energy from piston is absorbed partially or fully by retaining pins. - Prevalent in most applications: Bridge work,quarrying, or trenching.Failure of tool in slot area is caused by: - Worn lower tool bushing. - Worn retaining pins - usually with chisel tool.
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Fatigue -1
Starting point
Beach marks
Common Failure
Fatigue failure starts on surface from stress concentration points :- Scratches or gouges on working length .- Seizures in bushing areas or retaining pin slots.
Fatigue cracks are recognized by “Beach mark” patterns. - Semi circular marks around failure point.
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Fatigue -2Working Area
Beach marks
Failure occurring on working area outside lower tool bushing.Heavy gouges or scratches on surface create stress concentration points, leading to fatigue failure.Unexpected breakage can be attributed to: - High frequency with low loads.
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SEIZURESMost Common Failure
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Over 50% of Fatigue Failures are seizures in lower tool bushing area.• Seizures occur as tool slides against bushings or retaining pins.• Seizures are caused by: - Wrong working angle. - Insufficient grease. - Wrong type of grease - Improper greasing interval. • Fatigue failure results from stress concentration once crack is formed.
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Bushing Bushing Bushing
Tool Tool Tool
Friction heating Welding Crack
Signature mark(High lip)
• Bending stresses exceed material strength.• Excessive bending is caused by: - Prying with tool. - Wrong working angle. • High lip formation occurs in or near lower tool bushing.
BENDING.1#1 Failure caused by Operators
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BENDING.2
• Bending occurring inside lower bushing caused by: - Operator lifting and prying on tool stuck in material. • High lip formation occurs on bearing surface of bushing.
Inside bushing
Combination ofPrying while Lifting up
#1 Failure caused by Operators
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Mushroom affect
TOOL TIP Mushrooming
Chipped Edge
Hammering in one spot too long. - No tool penetration. - Produces higher heat loads on tip.Wrong working method.To small hammer for application.
Chipping caused by: - Improper contact with material. - Wrong selection of tool for application. Causes faster wear on retainer pins and tool slot.
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MODIFICATIONSWelding on Tools
DO NOT weld on tools Welding produces cracks on tool surface leading to fatigue failure.
Resharpening Tools• Tools are thru hardened.• Resharpen : - By milling. - By turning on a lathe. - By Sawing at low temperatures (Max 150 C / 300 F)
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Model A B C D E F
H115 10 30 20 60 24 142
H120 18 30 20 60 24 172
H130 20 30 20 60 24 197
H140 20 30 20 60 24 225
H160 20 30 20 60 24 230
H180 20 30 20 60 24 257
Chisel Moil
A min
B
C
D
F
E
RESHARPENING
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Tools are ultrasonic-tested to prevent such failures.
Manufacturing Defects
Failure starts under the surface and radiates out because of:- Impurities in steel- Weak spot in material.
Inclusion
Anywhere
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Extending Tool LifeGreasingLowers Owning & Operating Cost by: - Extended Tool life. - Extended Bushing life.
Greasing Interval
• Every TWO hours of machine operation. - Extreme conditions more often.• 20 - 30 strokes from grease gun.• Optimum for hammers an Autolube system.
Grease TypeCAT Multipurpose Molybdenum grease (MPGM) - Molybdenum based grease. - Dropping point over 250 C / 480 F - Grade equal to an NGLI Number 0...2 - Water resistant.
Inadequate greasing
Using Correct Working Methods
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